Intel 80386 processor family

CPU » 80386 family

The third x86 generation of x86 microprocessors, Intel 80386 (i386) was a 32-bit microprocessor backwards compatible with previous generations of 80x86 CPUs. Major new feature in the i386 CPU was 80386 protected mode - this mode fixed many shortcomings that existed in the 80286 processor and in the 80286 protected mode:

The 80386 mode included complete set of 32-bit registers and 32-bit instructions.
Although in this mode the CPU still used memory segment architecture similar to the one present in earlier x86 microprocessors, the size of memory segments was increased to 4 GB. This simplified development of 32-bit software, and in most cases applications could run without worrying about switching memory segments.
It became possible to switch from protected mode back to real-mode without simulating processor reset.

Another new mode in the 80386 CPU was 8086 virtual mode. In this mode the CPU could run old 8086 applications while providing necessary protection of memory and other resources. Introduction of this mode and 80386 protected mode was very significant step. All current 32-bit x86-based operating systems use these modes to run legacy 16-bit and more modern 32-bit applications.

There were a few different versions of the 80386 CPUs:

80386DX - this CPU could work with 16-bit and 32-bit external buses.
80386SX - low cost version of the 80386. This processor had 16 bit external data bus and 24-bit external address bus.
80386SL - low-power microprocessor with power management features, with 16-bit external data bus and 24-bit external address bus. The processor included ISA bus controller, memory controller and cache controller.
Embedded 80376 and 80386EX processors.

The Intel 80386 was produced at speeds up to 33 MHz, AMD produced even faster 40 MHz version.

Die pictures:

AMD A80386DX-40 Intel A80386DX-25 Texas Instruments TI486DLCE-40BGA

AMD

Picture of: AMD A80386DXL-20

20 MHz
132-pin ceramic PGA

AMD 80386DXL was a fully static microprocessor, object-code and pin-compatible with 80386DX CPU. The DXL processors had lower power consumption than Intel 80386DX CPUs. Power consumption could be reduced even further by reducing CPU frequency. If necessary, the CPU could be stopped completely without loosing the content of CPU registers. In this mode maximum power consumption of the CPU was less than 0.001 Watt.

Chips

Picture of: Chips J38600DX-25

25 MHz
132-pin ceramic PGA

Cyrix

Picture of: Cyrix Cx486DLC-33GP

33 MHz
132-pin ceramic PGA

IBM

Picture of: IBM 51F1784ESD

20 MHz (?)
132-pin PGA

Intel

Picture of: Intel NG80386SX-25

25 MHz
100-pin plastic QFP

Intel 80386SX microprocessor was a cost-effective version of the 80386DX. The SX processor had 16-bit external data bus - this allowed the CPU to work with cheaper 16-bit hardware, but at the same time it made access to 32-bit memory data slower. The 80386SX also had 24-bit address bus, which limited CPU's physical memory to 16 MB. Because the processor didn't work with 32-bit buses like the 80386DX, it didn't require as many signal pins. The 80386SX processors were manufactured in 100-pin package, or 32 pins less than the number of pins on DX package.